Nicotine alkaloid levels, and nicotine to nornicotine conversion, in Australian Nicotiana species used as chewing tobacco

Abstract

A range of endemic Nicotiana species are chewed as a smokeless tobacco by several Aboriginal populations of Australia. In tobacco research, nicotine to nornicotine conversion is important because nornicotine lowers tobacco quality and is detrimental to health. A diverse group of cytochrome P450 genes with different transcriptional regulations are involved in this conversion. The primary aims of this study were to quantify the pyridine alkaloids and investigate nicotine to nornicotine conversion in laboratory-grown Australian Nicotiana spp. Nicotine, nornicotine, anatabine, anabasine, myosmine and cotinine were quantified in fresh leaves of 24 out of the 26 recognised Australian Nicotiana taxa. Conserved regions of CYP82E related genes were PCR amplified in all studied taxa. The conversion process in fresh leaves was compared with that in leaves that underwent a simulated curing process for species that we identified as being high converters (N. cavicola, N. goodspeedii, N. velutina) and low converters (N. benthamiana, N. excelsior, N. gossei). Agarose gel electrophoretic analysis of CYP82E related genes obtained from the PCR amplification of the cDNA in fresh versus leaves with simulated curing showed about a 3-fold increase in transcript accumulation levels in cured leaves of the high converter species, while the transcript accumulation in N. gossei and N. excelsior maintained a steady basal level and increased by a small amount in N. benthamiana. This suggests the presence of functional loci that are triggered by curing in only high converter species and indicates a potential risk for chewers of high converter species.